Process for the production of iodide chromium



Dec. 31, 1963 A. c. LOONAM ETAL 3,116,144 PROCESS FOR THE PRODUCTION OF IODIDE CHROMIUM I Fil ed April 25, 1956 Iodine l7 AAA.

Furnace Winding John M. Blocher, Jr.

Alfred G. Loonam lNVENTORS ATTORNEY States ate dce Patented Dec 3 3,116,14 PROCESS FOR THE PRGDUC'HQN F HQDEDE CHRGMEUM Alfred C. Leonora, New York, N.Y., and .Fclin M. Bleacher, 312, Columbus, @hio, assignors, by direct and means to Chilean Nitrate Sales Corporation, New York, N.Y., a corporation of New York Filed Apr. 23, 1956, Ser. No. 57%,955 3 Claims. (Cl. IS-84.4)

This invention relates to the production of metallic chromium. More particularly, the invention contemplates the provision of an improved method or process for producing high'purity metallic chromium by dissociation of chromium iodides.

In recent years, a great deal of research has been corducted in connection with chromium met-llurgy in an effort to obtain high-purity ductile metallic omium and chromium-base alloys for general utilization in high-ternperature metallurgical applications because of its ready availability and high me ing point (1875 C). For example, the major constituent or alloying ingredient wi in presently preferred heat-resistant alloys is cobalt, but the relative scarcity of this metal and its low melting point 1495 C.), which seriously limits possibilities for significant improvements in cobalt-base alloys, emphasize desirability for obtaining chromium-base alloys. Certain chromium-base alloys produced heretofore have exhibited high-temperature strength greater than that of the cobaltand nickel-base alloys currently in use, but such alloys have had such poor room-temperature ductility that they are virtually useless for any practical purpose, whereas certain reported chromium-base alloys which exhibit some room-temperature ductility have not demonstrated particularly good high-temperature strength.

The primary factor underlying prior failures in at tempts to utilize unalloyed chromium and chromiumbase alloys for applications of the general class described, has been the extreme brittleness or lack of ductility at practical temperatures that has characterized so-called high-purity metallic chromium products heretofore available in industry. In point of fact, unlike titanium, zirconium, vanadium and molybdenum, once thought to be brittle but now known to be cold ductile metals and merely subject to loss of ductility upon contamination with slight amounts of impurities, it has been postulated by some researchers within the field of the present invention that absolutely pure metallic chromium is inherently brittle by nature, i.e., by reason of high melting point and its crystal structure, and, hence, not subject to improvement in ductility merely by application of improved recovery and refining techniques. Support for this theory is found in the fact that the highest-purity metallic chromium heretofore available commercially is extremely brittle at ambient temperatures and could not be worked by conventional techniques even at temperatures as high as 960 C.

While it might appear, in theory at least, based upon seemingly analogous research concluded heretofore with respect to the recovery of elemental titanium by dissociation of titanium tetraiodide (US. Patent Nos. 2,694,652, 2,694,653 and 2,694,654, issued to co-inventor Alfred C. Loonam on November 16, 1954), that the direct application of the classical Van Arkel-De Boer principles or hot-wire technique to the thermal decomposition of chromium iodides offers a potential commercial process for the production of high-purity metallic chromium, in practical application it is found that several basic differences defeat such a direct analogy. In the first place, the chromium iodides are found to have melting points in excess of 760 C. and are not amenable to transfer or llow as liquids at relatively low temperatures as is te case with titanium tetraiodide. Secondly, the chromium iodides have relatively low volatility; chromous iodide (Cfl -MIP. 856 C.), for example, must be heated above 590 C. to get appreciable quantities of the compound in the vapor phase. Furthermore, the iodides of chromium are found to be so unstable that decomposition occurs at temperatures not much in excess ol those required to maintain appreciable quantities of the iodides in the vapor phase.

in the application of the V an Arlrel-De Boer technique to chromium recover, relatively impure chromium metal and a small quantity of elemental iodine (or chromium iodides) are placed in a reaction vessel housing a wire filament of tungsten or molybdenum, and the vessel is then evacuated, sealed off, and heated to a temperature at whi h c romium iodide may be formed readily by reac- 0 mental iodine with the impure metallic chromiwhile the wire filament is heated to a higher temperal ll, ure at which the chromium iodide thus produced may be decomposed. In operation, iodine liberated from the chromium iodide upon decomposition of the iodide at the filament, reacts with the impure metallic chromium at the lower temperatures within the reaction vessel to form additional chromium iodide which is in turn decomposed at the filament, and so on. In theory at least, the iodine functions as a carrier to extract chromium from its impurities.

Upon actual application of the foregoing Van Ark-el- De Boer or hot-wire technique in efforts to dissociate chromium iodides for the production and deposition of high-purity metallic chromium on wire dissociation filamerits formed of various materials, we have found that the reaction proceeds extremely slowly, with frequent fiic merit failures at the temperatures involved, and that the chromium deposits thus produced consist of coarsely crystalline, brittle, spiny structures which retain their inherent brittleness following arc-melting for the formation of ingots. Furthermore, because of the highly non-uniform nature of these deposits it is virtually impossible to maintain constant filament temperatures even with very close supervision and regulation of the applied voltage to the dissociation filament during operation of such a De Boertypc unit.

The process of the present invention is based, in part, on the overall results of our investigations which establish the ductility of chromium metal is, in fact, a function or" its relative purity with respect to certain non-metallic impurities such as oxygen, carbon and nitrogen, and certain metallic impurities, principally nickel, but including iron, aluminum and other metallic impurities as well. The process of the invention is also based in part upon our discovery of improved methods and procedures whereby coherent deposits of high-purity, cold-ductile metallic chromium can be produced in commercial yields by dissociation of chromium iodides and deposition of elem n-tal chromium on an indirectly-heated amorphous dissociation surface. Thus, we have found that in lieu of the conventional Van Arkel-De Boer wire filaments, coherent deposits of chromium may be produced and recovered readily from dissociation elements comprising heated rc-entrant tubes, consisting of an internal bayonet-type heating element surrounded by an external deposition surface formed of a refractory amorphous substance such as quartz, hig -silica glass (i.e., Vycor, trademark, among others), or silica, which may be coated to facilitate removal of deposited chromium, as, for example, with a very thin layer of graphite. The fact that relatively coherent deposits of high-purity chromium metal may be made and subsequently recovered in pure form from an oxide-containing deposition surface such as quartz, for example, is unique and totally unexpected for the reason that at the temperatures involved and in the presence of the reagents involved one would expect a high degree of contamination to result from reaction of chromium with the deposition surface or from slight attack of silica by iodine :or iodides. Not only are the overall yields and physical characteristics of the deposited chromium enhanced through use of such a dissociation and deposition element, but the resulting system does not require the constant attention and control necessary in conventional hotwire-type operations for the reason that the deposition element is entirely independent of the electrical circuit. Furthermore, the disadvantages attendant to burnout of conventional hot-wire filaments and the metallic-core contamination of products recovered from such prior operations are eliminated within the process of the invention. While quartz, silica and highilica glass have been employed exclusively within the process of the invention, it is believed that other ceramic substances of high chemical stability, such, for example, as alumina refractories like Alundum (trademark) or porcelains should function equally as well.

Briefly, the process of the invention utilizes the static Van Arkel-De Boer bulb technique modified by the fore going principles, as will appear more fully from the following detailed description of a specific embodiment of the invention taken in conjunction with the accompanying drawing, wherein the single FEGURE illustrates a typical dissociation unit employed in practicing the invention.

VJith reference to the drawing, the dissociation apparatus comprises a suitable reaction vessel It; formed of quartz, high-silica glass, silica, or a similar ceramic material of high chemical stability, or any relatively inert iodine-resistant metal such as molybdenum, or an alloy of sirnilar inert, corrosion resistant properties. Conveniently, the reaction vessel may be made of the same amorphous substance employed as the deposition surface which can then be formed as a re-entrant surface of the overall vessel, such as the re-entrant tube lll illustrated in the apparatus of the drawing, since deposition of chromium in accordance with the process of the invention is offected at temperatures at which such substances can be employed. Alternatively, reaction vessel It and the dissociation and deposition element ill can be formed as independent units and provided with suitable removable mounting and sealing arrangements. In lieu of direct deposition on the re-entrant tube, the tube may be fitted with a deposition sleeve or sheath of quartz, high-silica glass or silica to receive the metallic chromium deposits, as illustrated by sheath 11a within the embodiment illustrated in the drawing. Thus, since the chromium deposits are relatively difficulty removable from the deposition surface, such an arrangement provides an ideal recovery technique. Furthermore, sheaths of the'type of 11a may be employed in conjuntion with metallic deposition vessels provided with one or more metallic rte-entrant heating tubes, such as tube 11 illustrated in the drawing, whereby the relatively inexpensive amorphous sheaths function to receive the chromium deposits on a production basis, with the sheaths simply being replaced for each operating cycle. Here again, it is believed that sheaths formed of other high-stability ceramics, such as alumina refractories and porcelains, may be employed in practicthe process of the invention. Furthermore, it is believed that similar deposition media formed of metallic chromium would function admirably well for purposes of the invention. The deposition sleeves or sheaths 11d should extend beyond the point on the main heating tube 11 where deposition normally occurs to avoid possible adhesion upon cooling, or damage to the heating tube due to differential contraction upon cooling, and should be closefitting but not tight.

The reaction vessel It: is fitted with a perforated cylindrical sleeve 12, preferably formed of molybdenum, and adapted to retain metallic chromium feed or charge material l3 distributed around the periphery of the vessel. The dissociation-deposition surface or re-entrant tube 11 is heated by means of a bayonet-type resistance heater consisting of winding r14- mounted on an insulated support 5. The reaction vessel is provided with an exhaust port 16 for outgassing the system, and a suitable container 17 for an initial supply of chromium iodide or a supply of elemental iodine used in preparing an initial charge of chromium iodide.

In operation, vessel 10 is charged with metallic chromium 13 and the top of the vessel is then sealed by fusion or any other suitable means, and a supply of elemental iodine or of chromium iodide is placed in container 17. The exhaust port 16 is connected to a vacuum system and the unit is then hot-outgassed under vacuum while the vessel 1'7 containing chromium iodide or iodine is maintained at a temperature low enough to prevent significant evaporation of these substances. Thereafter, constriction 18 (or an equivalent valve arrangement) is closed; conveniently by cooling with Dry Ice to form a plug of condensed iodine or chromium iodide. The elemental iodine in container '17 is then vaporized into reaction vessel 10 to form chromium iodide, and the system is hot-outgassed under vacuum again with similar precautions being exercised to avoid loss of chromium iodide by evaporation. The system is then sealed by fusion, as by means of restriction 19 shown in the drawing or any suitable valve arrangement, and the vessel 10 is heated to a temperature with the range 550-900 C. in a suitable oven or furnace (winding shown), while the re-entrant tube 11 and c0- operating shreath 11a are heated to a higher temperature Within the range 7501100 C. for deposition of elemental chromium on the sheath as indicated by reference numeral 20 in the drawing. At the end of a run, the reaction vessel is cooled to room temperature and opened for recovery of deposited chromium. It is highly desirable that the reaction vessel heating means (winding shown) he de-energized before the tube is cooled in order to prevent condensation of chromium iodide on any part of the deposited chromium. The chromium deposit is recovered from the re-entrant tube or sheath.

Studies of the effect of various re-entrant tube (11) and reaction vessel (10) temperatures on the rate of deposition of chromium have demonstrated that the rate can be doubled by increasing the tube temperature from 850 C. to approximately 900 C. at a constant vessel temperature of approximately 700 C. A tube temperature of 1000 C. results in a higher deposition rate than that obtained at 900 C. With the reaction vessel maintained at a temperature of approximately 800 C. On the other hand, upon increasing the tube temperature to 1100 C. and higher, no further increase in deposition rate was obtained at cor-1st nt vessel temperatures of 700 C. but rather, the deposition of chromium was found to be heavier on cooler portions of the tube. In a similar manner, when the temperature of the reaction vessel was increased from 700 C. to 800 C. with constant tube temperatures of approximately 900 C., no significant increase in the deposition rate was obtained. Accordingly, in actual practice for optimum rates of deposition We prefer to operate at reaction vessel temperatures within the range 600800 C. and at tube temperatures with- The tabulated examples set forth hereinafter demonstrate the preparation of typical iodide chromium products in accordance with the foregoing principles of our invention.

in the range 9004050 0, although the system will op- 5 A 200 gram lot of iodide chromium obtained by the crate at lesser efficiencies with substantially any tenipera process of the invention was arc-melted and fabricated inture differential between the reaction vessel and deposito two 4-inch pieces of 0.20 5-inch diameter which were tion surface over the range from 550410- C. stress-relief annealed. A reduced section (0. inch X I It has been found, quite surprisingly, that the deposi- 0.75 inch) was ground in one rod which was tested at tion rate can be increased by a factor of from three to 10 room temperature in tension at a cross-head speed of five and the purity of the deposited chromium improved 0.005 inch per second. The results are presented in significantly if, in lieu of sealing the reaction vessel from tabulated form below: the vacuum system as described above, it is left con- TABLE I nected allowing a plug of chromous iodide to form in the connecting line. Moreover, it is further found that it is desirable to vaporize or flame this plug from the Property Performance line periodically and permit it to reform. Any other T f S d 1 tonne specimen WENQ IO( suitable mechanical closure functioning in the same man- 01% ffset, yield strength si). nor should produce equivalent enhanced results. In purg- 0. ns t y ld str h (p. 1) 2% 888 mg the system in this manner, the vapor pressure of the 44 chromous iodide being relatively low, it pract cally all Reduction in area (percent) 78 remains within the reaction chamber. The beneficial effects of such periodic outgassing of the system ar ap- The other specimen was used in dynamic modulus parently attributable to the removal of accumulated measurements at temperatures up to 1500 F. With the gaseous or volatile impurities from the reaction vessel. results shown in tabulated form below:

There is no apparent critical pressure limitation with- TABLE II in the chromium iodide system of the invention, and fair deposition rates have been obtained at various pressures Temperature, F: Modulus, 10 psi. up to 200 mm. of mercury under suitable temperature 40' -2.7 conditions. The foregoing as well as other phenomena and characteristics of the system of the invention are demonstrated in greater detail within the examples presented hereinafter.

The chromium feed material or charge to reaction vessel 10 may consist of a relatively crude product capable of reacting with iodine to form chromous iodide, or such a product which has been subject to some prior refining or purification treatment. Thus, electrolytic chromium provides an excellent starting material as does chromium of the type obtained by aluminothermic reduction 4 techniques. The chromium feed material may be sub- Examples Sleeve dep- Vessel 'Iube Run Deposit Depo- Weight No. osition Temp, Temp, Time, Weight, sition of Kind of Vessel Remarks Surface 0. 0. Hrs. g. Rate, Feed, Cr Feed Size 1 g./lir. g.

700 900 117 36 0308 350 Elec A System Scaled. 725 900 147 409 274 793 E1000. A System plugged (CrIg) but not flamed. 750 900 137.5 548 Plugged and Flamed. 750 1,000 176 1, 511 D0. 750 1,000 125 1,140 Do. 800 1,000 125 1,060 Do. 800 1, 000 154 1,242 Do. 800 1, 000 150 1,302 Do. 7% 1, 000 125 554 System Sealed. 800 1,000 125 837 System lgluggod but not diameter, 2% inches; Length of deposition area, 8 inches.

area, 13 inches.

jected to one or more conventional purification treatments prior to charging to the reaction vessel in order to reduce the content of a particular impurity or impurities, as, for example, carbon or hydrogen treatment for deoxidizing purposes.

The iodide chromium products obtained by the process of the invention contain on an average of less than one hundred parts per million of nonmetallic impurities and less than fifty parts per million of metallic impurities. They are markedly superior to all other forms of socalled pure chromium heretofore available to industry and exhibit excellent room temperature ductility. The physical characteristics of the as-deposited chromium products of the invention may be further enhanced by appropriate Working schedules as demonstrated within the test data presented hereinafter.

BVcssellcngth, 16 inches; vessel C-Vessel length, winches; Vessel diameter, 4 inches; length of deposition I is to be understood that the specific embodiment of our invention described above and illustrated in the drawing is offered for purposes of illustration only. It will be obvious that there are many modifications and variations of the process which are practical, yet still within the realm of our invention, and it is intended that these be included Within the scope of our invention as defined within the following claims.

We claim:

1. Process for the production of metallic chromium that comprises passing gaseous iodine into contact with chromium-bearing material within a reaction vessel maintained at an elevated temperature to form chromium iodide, sealing the reaction vessel and maintaining the reaction vessel under constant exhaust conditions through a plug of condensed chromium iodide and periodically removing the plug and permitting it to reform, vaporizing the chromium iodide at a temperature Within the range 5'5090-0 C., decomposing the chromium iodide in the vapor phase by means of an indirectly-heated amorphous surface disposed Within the reaction vessel and formed of a substance selected from the group consisting of silica, quartz and highsilica glass maintained at a higher temperature within the range 75)1100 C. with the production and deposition of metallic chromium on the amorphous surface and the production of a gaseous product containing elemental iodine, and reacting the gaseous product within the reaction vessel for the icdination of additional chromium-bearing material.

2. Cyclic process for the production of high-purity metallic chromium that comprises passing gaseous iodine into contact with chromium-bearing material Within a eaction vessel maintained at a temperature Within the range 550900 C. to form chromous iodide, sealing and maintaining the reaction vessel under constant exhaust conditions through a plug of condensed chromous iodide and periodically removing the plug and permitting it to reform, decomposing the chromous iodide in the vapor phase by means of an indirectly-heated amorphous surface formed of a substance selected from the group consisting of quartz, silica and high-silica glass disposed Within the reaction vessel and maintained at a higher temperature Within the range 750-110 0 C. with the production and deposition of metallic chromium on the amorphous surface and the production of a gaseous product containing elemental iodine, reacting the gaseous product with the chromium-bearing material for the production of additional quantities of chromous iodide and subjecting the chromous iodide thus produced to dissociation by means of the heated amorphous surface with deposition of additional metallic chromium thereon.

3. In a process for the cyclic production of metallic chromium by dissociation of chrornous iodide vapors in contact with a heated dissociation and chromium-deposition surface disposed within a sealed reaction vessel also provided with a charge of chromium-bearing material for reaction with gaseous elemental iodine liberated during dissociation for the production of additional quantities of chromous iodide, the improvement that comprises maintaining the reaction vessel under constant exhaust conditions through a plug of condensed chromous iodide which is periodically removed and permitted to reform; whereby the reaction vessel is periodically outgassed without removing any significant quantity of chromous iodide present therein.

References Cited in the file of this patent UNITED STATES PATENTS 2,551,341 Scheer et al. May 1, 1951 2,606,955 lerrick Aug. 12, 1952 2,694,654 Loonam Nov. 16, 1954 2,717,915 Shapiro et a1 Sept. 13, 1955 2,739,566 Shapiro et al Mar. 27, 1956 2,756,043 Fleiszar et a1 July 24, 1956 2,768,074 Stauffer Oct. 23, 1956 FOREIGN PATENTS 698,234 Great Britain Oct. 14, 1953 562,616 Germany Oct. 27, 1932 OTHER REFERENCES Campbell et al.: Trans of the Electrochem. Soc, vol. 96, No. 5, pp. 318-333.

Metal Industry, October 8, 1943, pages 283286. 

3. IN A PROCESS FOR THE CYCLIC PRODUCTION OF METALLIC CHROMIUM BY DISSOCIATION OF CHROMOUS IODIDE VAPORS IN CONTACT WITH A HEATED DISSOCIATION AND CHROMIUM-DEPOSITION SURFACE DISPOSED WITHIN A SEALED REACTION VESSEL ALSO PROVIDED WITH A CHARGE OF CHROMIUM-BEARING MATERIAL FOR REACTION WITH GASEOUS ELEMENTAL IODINE LIBERATED DURING DISSOCIATION FOR THE PRODUCTION OF ADDITIONAL QUANTITIES OF CHROMOUS IODIDE, THE IMPROVEMENT THAT COMPRISES MAINTAINING THE REACTION VESSEL UNDER CONSTANT EXHAUST CONDITIONS THROUGH A PLUG OF CONDENSED CHROMOUS IODIDE WHICH IS PERIODICALLY REMOVED AND PERMITTED TO REFORM; WHEREBY THE REACTION VESSEL IS PERIODICALLY OUTGASSED WITHOUT REMOVING ANY SIGNIFICANT QUANTITY OF CHROMOUS IODIDE PRESENT THEREIN. 